After installing blank theme in magento,an error will appear like this,
Fatal error:Call to a member function toHtml() on a non-object in /app/code/core/Mage/Core/Model/Layout.php on line 529
To fix this error,go to /app/design/frontend/default/blank/layout/ and open page.xml file.
Find the code around line no 89, which looks like this,
<block type="core/profiler" output="toHtml" />
Change it to
<block type="core/profiler" output="toHtml" name="core_profiler"/>